AERCO BMK 2.0 LN Dual Fuel Nov 2010 - Manual (Page 31)

CONTROL PANEL OPERATING PROCEDURES
3.9 START SEQUENCE
When the Control Box ON/OFF switch is set to
the ON position, it checks all pre-purge safety
switches to ensure they are closed. These
switches include:
• Safety Shut-Off Valve Proof of Closure
(POC) switch
• Low Water Level switch
• High
Water Temperature switch
• High Gas Pressure switch
• Low Gas Pressure switch
• Blower Proof switch
If all of the above switches are closed, the
READY
light above the ON/OFF switch will light
and the unit will be in the Standby mode.
When there is a demand for heat, the following
events will occur:
NOTE
If any of the Pre-Purge safety device
switches are open, the appropriate fault
message will be displayed. Also, the
appropriate fault messages will be displayed
throughout the start sequence, if the
required conditions are not observed.
1. The DEMAND LED status indicator will light.
2. The unit checks to ensure that the Proof of
Closure (POC) switch in the Safety Shut-Off
Valve (SSOV) is closed. Figure 3-3 shows
the Natural Gas SSOV location for a Factory
Mutual (FM) Gas Train.
3. With all required safety device switches
closed, a purge cycle will be initiated and the
following events will occur:
(a) The Blower relay energizes and turns
on blower.
(b) The Air/Fuel Valve rotates to the full-
open purge position and closes purge
position switch. The dial on the Air/Fuel
Valve (Figure 3-4) will read 100 to
indicate that it is full-open (100%).
NATURAL
GAS INLET
PROPANE
INLET
TO
AIR/FUEL
VALVE
NATURAL
GAS SSOV
PROPANE
SSOV
Figure 3-3.
FM Gas Train SSOV Locations
4. Next, the blower proof switch on the Air/Fuel
Valve (Figure 3-5) closes. The display will
show Purging and indicate the elapsed time
of the purge cycle in seconds. The normal
(default) time for the purge cycle is 12
seconds.
Figure 3-4.
Air/Fuel Valve In Purge Position
3-9